KAJIAN FISIOLOGIS DAN AGRONOMIS KETAHANAN KEKERINGAN VARIETAS TANAMAN JARAK PAGAR (Jatropha curcas L.) DI LAHAN PASIR PANTAI DI KABUPATEN PURWOREJO

I Gusti Made Arya P., Ir.,M.App.Sc., Prof. Dr. Ir. Didik Indradewa,Dip.Agr.St.

2011 | Disertasi | S3 Agronomi

Tanaman jarak pagar merupakan tanaman tropis penting penghasil biofuel dan terkenal karena ketahanannya terhadap kekeringan, namun penelitian tentang kemampuannya untuk tumbuh dan berkembang di bawah kondisi kekeringan masih sangat jarang diteliti. Oleh karena itu, sifat fisiologis dan agronomis cekaman kekeringan tanaman jarak pagar, serta mekanisme ketahanan kekeringannya di lahan pasir pantai dikaji dalam penelitian ini. Screening di pembibitan berdasarkan pada laju pertumbuhan vegetatif dan berat keringnya terhadap 9 varietas dilakukan untuk mengelompokkan menjadi varietas yang tahan dan tidak tahan, dan interval penyiraman yang menyebabkan cekaman kekeringan dan pertumbuhan optimum. Varietas terpilih yaitu IP-1A, IP- 2M (mewakili varietas tahan), Unggul Lokal dan Daun Kuning (mewakili varietas tidak tahan) ditanam di lahan pasir pantai yang disiram 3 dan 9 hari sekali untuk dikaji sifat fisiologis dan agronomisnya. Di samping itu, juga dilakukan pengujian terhadap potensi daya hasilnya di lahan pasir pantai. Hasil penelitian menunjukkan bahwa varietas IP-1A merupakan varietas yang paling tahan dan sesuai untuk dikembangkan di lahan pasir pantai berdasarkan sifat fisiologis dan agronomisnya. Pada tahun pertama, varietas IP-1A menghasilkan 33,54 g biji kering/tanaman (setara dengan 0,15 ton/ha). Cekaman kekeringan menurunkan kadar air sel daun, kadar air nisbi daun, potensial air daun dan kelembaban nisbi daun tanaman, meningkatkan suhu sel dan suhu permukaan daun, menurunkan kerapatan, bukaan dan konduktivitas stomata, laju transpirasi, kadar CO2, kadar klorofil, laju fotosintesis, tetapi meningkatkan kadar prolin dan asam absisat daun, menurunkan tinggi tanaman, diameter batang, dan jumlah daun, indeks luas daun, serapan cahaya, total panjang, luas permukaan, dan diameter akar, meningkatkan ratio akar tajuk dan menurunkan berat kering tanaman. Jumlah daun dan kadar klorofil daun merupakan parameter pendukung langsung terhadap berat kering tanaman. Mekanisme ketahanan kekeringan tanaman jarak pagar di lahan pasir pantai adalah menghindar (avoidance strategy).

Jatropha, an important tropical bio fuel crop, is reputed for its drought resistance, however, number of research working on its ability to perform under dry conditions was little. Therefore, the physiological and agronomical aspects of its drought stress, and drought resistance mechanism under that conditions were studied in this research. Screening during seedling period on 9 genotypes, based on their vegetative growth rate and plant dry weight, was carried out to classify them into resistant and susceptible genotypes to drought stress, and to determine watering intervals causing drought stress and optimum growth. The selected genotypes, such as IP- 1A and IP-2M (representing resistant genotypes), and Unggul Lokal and Daun Kuning (representing susceptible genotypes), were planted in coastal sandy land conditions watered once in 3 and 9 days to study their physiological and agronomical aspects. In addition, they were also grown to evaluate their yield potency in that conditions. The result showed that IP-1A was the most resistant genotype and suitable to develop under coastal sandy land conditions, based on its physiological aspects, vegetative growth, and yield. In the first year, IP-1A produced 33.54 g of seed/plant (equal to 0.15 ton/ha). Drought stress reduced water content of leaf cell, leaf relative water content, leaf water potential, and leaf relative humidity, increased leaf cell and surface temperatures, reduced stomatal density, aperture, and conductivity, transpiration rate, CO2 and chlorophyll content, photosynthetic rate, increased leaf prolin and abcisic acid contents, reduced plant height, stem diameter, number of leaf, leaf area index, light absorption, root length, surface width and diameter, increased root shoot ratio, and reduced plant dry weight. Number of leaf and chlorophyll content were directly supporting parameters on plant dry weight. Drought resistance mechanism of jatropha under coastal sandy land conditions was avoidance strategy.

Kata Kunci : Tanaman jarak pagar, biofuel